1. Field of the Invention
The invention relates to a check valve controlled by differential pressure, preferably in the form of a disk valve, whereby a closing element impacts a valve seat with force by means of an elastic (resilient) element, preferably a closing spring.
2. The Prior Art
Aside of mechanically actuated valves for high-pressure fuel injection, particularly for large-volume combustion engines, hydraulically actuated valves have also been used in the past. One possibility to avoid the disadvantages of the above-mentioned (valve) solutions is high-pressure metering by means of a gaseous fuel injector, which has found increasing importance in recent times and which consists of a combination of an electro-magnetically actuated metering valve and a valve controlled by differential pressure. As long as the metering valve is closed, the check valve is pushed against the (valve) seat by its closing spring and dependably seals thereby the fuel delivery system from the combustion chamber. After opening of the metering valve, the valve body of the check valve is opened again by the applied gas pressure. Such gaseous fuel injectors are suitable for injections with currently common gas pressures of 1 to 3 bars above the suction pressure and they are suitable as well for high-pressure injections of 20 to 60 bars above the suction pressure. However, the traditional (valve) solutions are marked with the disadvantage of a free movement of the closing element in the check valve. In addition, the check valve rebounds once or several times before reaching its stationary end-of-travel position since the impact occurs in the form of partial elastic impact shocks caused by the elasticity of the dynamic system. This reduces the metering precision of the valve on one hand and on the other hand there is the danger of undue wear by micro-friction in the region of impact.
U.S. Pat. No. 4,964,391 discloses damping of the valve movement of a check valve for a fuel delivery system in combustion engines alone for its vibration reduction and for its reduction of pressure pulses; however, it is designed as a piston-cylinder unit that is connected to the valve element.
Another configuration of a check valve is described in SU-A-892084 wherein it is to be effective in the area of a flame-blocking connection and it uses for the purpose of damping of the closing shock a valve seat that is pre-tensioned by means if a spring. In addition, there are known from different patent documents, e.g. EP-A-0 195 261, EP-A-0 628 137, EP-A-0 628 137, WO91/03641 and EP-A-0 411 041, various movement and impact damping (buffer) devices in valves and also in fuel delivery systems, which influence impact surfaces, hydraulic buffers and elastic (resilient) connections of the moved masses.
It was the object of the present invention to provide a check valve controlled by differential pressure of the type mentioned in the beginning whereby the closing shock is damped in a manner whereby the closing element does not rebound even once or several times. An additional object of the invention was also the damping of the opening shock of a valve of this type. Another object was to provide a wear-resistant gaseous fuel injector consisting of a pilot valve and a check valve with a high degree of metering precision.
For the achievement of the first object, according to the invention, the closing element is provided with an additional mass that is greater than the mass of the closing element itself. Thereby acceleration of the valve element and the impact force remain low at both end-of-travel positions. The danger of wear by micro-friction (fretting) in the region of impact of the valve element and valve seat is thereby considerably reduced. Finally, recurring rebounding (one or more times) of the valve element from the valve seat before reaching the two stationary end-of-travel positions is avoided so that the metering precision of the check valve is substantially increased.
According to a special embodiment of the invention, the check valve is provided with a closing element which consists of a disk-shaped or mushroom-shaped segment cooperating with the valve seat and a stem attached thereon onto which a closing spring acts upon. For achievement of the present object, the embodiment is characterized in that the additional mass is designed as a projecting receiving element for the closing spring disposed at the end of the stem. Thereby an already existing element may be used to dampen the opening and closing shock without substantial enlargement of the necessary structural space.
According to an additional characteristic of the invention, at least one part of the added mass is coupled with the closing element via a damping ring so that during impact in the closed end-of-travel position of the check valve, the total impact energy does not have to be dissipated within the valve seat and whereby the modulus of elasticity of the damping ring is lower than the lower modulus of elasticity of the closing element and the additional mass.
According to an advantageous embodiment it is proposed that the closing element and the additional mass are made of steel and that the damping ring has a lower modulus of elasticity than the utilized steel.
To improve damping of the opening shocks and especially to avoid detrimental effects of the impact force, the check valve is characterized according to one of the above paragraphs in that at least one or each elastic deformable stop element made of reinforced synthetic material.
In a design modification of a check valve according to the invention, at least one impact element is designed as a stop ring embracing the valve stem onto which stop ring the receiving element for the closing spring makes contact in the open end-of-travel position of the check valve. The closing element consists of a disk-shaped or mushroom-shaped segment cooperating with the valve seat and a stem attached thereon onto which a closing spring acts upon, and whereby a projecting receiving element is provided at the end of the stem.
Not to exceed the permissible operating temperatures in the region of the parts designated for impact damping, which are preferably made of synthetic material, it is proposed according to an additional characteristic of the invention that the stop ring is fitted directly to a guide bushing for the stem whereby said guide bushing is made of highly heat-conducting material, preferably sintered bronze. Therefore the major portion of the heat transferred to the closing element of the check valve may be dissipated through the stem and the valve body.
Borings are provided around the guide bushing as passages for the medium to achieve additional cooling of the stem of the valve element.
The last object pertaining to a wear-resistant gaseous fuel injector with high metering precision is achieved with a configuration that, according to the invention, consists of a magnetically actuated pilot valve and a check valve controlled by differential pressure that is disposed downstream thereof and which is designed according to one of the above paragraphs.
In the following description and with reference to the accompanying drawing a preferred embodiment example of the invention is described in more detail.